Stimulation using dry acid slurry



1 t) u a t tthih tetttr str United States Patent 1 2 as" F permanent plug. However, this is very difficult to do be- 3,417,817 cause communication behind the liner permits the plug- STIMULATION USING DRY ACID SLURRY John P. Moore, Metairie, La., assignor to Shell Oil Company, New York, N.Y., a corporation of Delaware ging agent to flow into the oil sands where plugging is not desired. Mechanical means or use of fluids of varying viscosities and el-set times to control the flow of plug- No Drawmg' Flled.Aug' 1967 659043 5 ging agents beliind the liner are generally unsuccessful 7 Chums (CL 166-30) and in addition are costly and difiicult to control and place or remove if necessary or desirable. Thereffore to i selective] lu permeable productive zones of orma-: ABSTRACT OF THE DISCLOSURE tionsand th ereifter treat the less permeable areas thereof A P for stimulation of underground fm'mations 10 by acidization or other suitable means so as to render the having hetlogeheous Permeable Produiiti"e Zones utiliz' formation essentially uniformly permeable on removal of ing a technique to temporarily but selectively plug porthe plug is diffi lt to achieve. tions of the'formation with a solid acidic material readily It is an object of the present invention to recover h susceptible to chemical dissolution, acidizing the less perdrocarbon fl id fig or il, f d tiv zones, meable productive areas and thereafter unplugging the Oi1 bearing Zones, by an improved process f SelectcihPoTaiily Plugged areas in the Productive Zone by tively but temporarily plugging certain highly permeable chemical dissolution and, thereby, improve the recovery Zones in the Productive Zones of h formations, of oil therefrom Still another object of the present invention is to temporarily plug heterogeneous productive zones without essentially plugging less permeable productive zones there- This invention is directed to a new, novel and improved f Process for recovering economically and efiectively Y' Still another object of the present invention is to temdiocarboh fluids, gas ahd/or from underground porarily plug the highly permeable oil-productive zones formations having heterogeneous Permeability More P with a dissolvable solid acidic plugging material and ticularly, the Present invention is diiected to a Process for thereafter increasing the permeability of the less permeimproving the recovery of liquid hydrocarbons from such able areas b idi i f rmati ns y temporarily sealing of plugg ng, h more Still another object of this invention is to temporarily permeable sections of the formations in order of decreasl a heterogeneous permeable oil-productive zone with ihg P a y with a supersaturated solution of ry a dissolvable solid acidic plugging material, acidizing the solid acidic Plugging or diverting material which is readily less permeable areas and thereafter removing the plugging dissolvable or chemically disintegratable. The heterogematerials by acid dissolution so as to render the entire neous permeable temporarily plugged areas of the oil or productive zone essentially uniformly permeable. gas productive zone are then acidized to render said for- Still anoth r obje t of the present invention is to remation more uniformly permeable, thereafter removing cover oil from oil-productive zones of a formation using the temporary plugging material and finally restored t0 fluid drives by first temporarily plugging the oil-produca producible status for hydrocarbons by suitable means tive zones with a solid acidic material subject to dissolusuch as backflow or injection-production techniques. tion by chemical action, removing portions of' the plug Background of the invention from the less permeable areas by acidization, thereafter 40 removing completely the temporary plug by chemical dis- The Problem of selective Plugging of formations to solution and finally recovering oil therefrom byuse of a P oil and gas recovery is well known in the art as fluid drive injected into'said now essentially uniformly evidenced y reference to Patents permeable oil-productive zones through an injection well 2,787,325, 3,261,400 and 3,141,503- In g by use of backflow or thrbugh a production well. eral, the entire permeable zone is plugged with a uni- 1 form plugging material and thereafter the less permeable Summary the mventlon zones are treated in a suitable manner so as to render Briefly stated, the process of the present invention comthem more permeable such as by acid treatment or the prises improving hydrocarbon recovery from .heterogelike. Under known conventional conditions it is frequently neous productive zones of underground formations and an extremely diflicult and costly procedure to subsequently prevents gas or water coming and loss of fluid-{drive due remove the plugging material from desired productive to fingering and the like by temporarily plugging the zones for subsequent recovery of oil. highly permeable zones of such formations with a super- In many situations it is common practice to drill saturated acidic solution containing dry solid acidic math h ll il d i Zones, cement d perforate terials, thereafter increasing the permeability of areas in casing so as to produce all zones simultaneousl I th r the productive zone by acidization or other suitable means cases, sand production is a problem and special liners to and finally removing the p 'y P g material exclude sand are hung through the productive intervals from the heterogeneous Productive Zohes y chemical or zones rather than to cement and perforate casing. In solution of the solid acidic P g material so as to other instances it is a production practice to place a render the Productive Zohe essentially uniformly P gravel filter between a screened liner and the perforated 0 able thereby Preventing fluid drive losses and improving casing to exclude sand. In liner completions, it is often and increasing hydrocarbon TecoVel'yy a supersaturated very difiicult, if not impossible, to successfully conduct acidic solution containing dry solid acidic materials is recovery operations when one of the zones is mor permeant an acidic solution preferably an aqueous acidic meable than other portions of the oil sand. As a result, medium supersaturated with a 'y acid which y he the displacing fluid, such as steam, gas or Water, channels 5 in flake, Particle crystalline form in which h ndisquickly through thief zones or depleted permeable zones solve-d acid "articles act as the diverting or temporary or results in water or gas coning resulting in poor dis- Plugging agentsplacement in the remainder of the oil sands.

In heterogeneous permeable formations and particu- Descnpnon of the f i embodiments of larly those with thief zones, it is generally necessary to the invention inject a compound into the more permeable section particularly in the vicinity of the borehole so as to create a As stat d above, the process of the present invention comprises: (1) either temporarily plugging the more permeable zones of a heterogeneous permeable productive zone with a supersaturated solution of dry acid or (2) temporarily plugging the entire permeable productive zone and thereafter acidizing the less permeable areas so that on chemical dissolution of the temporary plug the entire productive zone is rendered essentially uniformly permeable.

To acccimplish the essence of the process of the present invention the essential steps comprise:

Injecting a supersaturated solution of a dry acid containing substantial amounts of solid dry acid particles suspended therein in a well borehole and into a hydrocarbon productive formation zone to be treated;

Maintaining said solution therein for a time suflicient to preferably temporarily plug the more permeable areas or the entii'e permeable zone;

Injecting an acidizing fluid into the formation to increase the; permeability of the less permeable area of the formation;

Continuing acid injection until the temporary plug of dry acid is dissolved; and

Recovering hydrocarbons therefrom by suitable means, preferably by a drive fluid.

Dry acids useful to form supersaturated solutions or slurries of the present invention can be any dry acid which in a supersaturated solution contains substantial amounts of solid acid in the solution or slurry and includes sulfamic, glycollic, fumaric, oxalic, citric, tartaric, p-hydroxy'benzonic acids and the like, some of which are commercially available under the trade names of Visco 900 or Instant Acid obtained from Visco Chemical Company and Dowell, respectively.

The solvent or carrier liquid for the dry acid can be an acidic aqueous or hydrocarbon liquid such as water acidified with hydrochloric acid, e.g., a -30% HCl water solution. Illustrative examples of temporary plugging compositions are as follows: (A) 15% dilute HCl aqueous solution supersaturatedwith sulfamic acid; (B) 15% dilute HCl aqueous solution supersaturated with glycollic acid; (C) 15% HCl solution containing 2.5 lb./ gal. of :sulfamic acid; (D) aqueous solution of super mud acid (9% HCl and 6% HF) supersaturated with sulfamic acid and (E) 15% dilute HCl aqueous solution supersaturated with oxalic acid.

Acidizing with an undersaturated solvent to remove part or the entire temporary plug can be accomplished by using suitable acidization techniques. The acidizing process can be accomplished by using any acidic material, which can be either gaseous or liquid, capable of dissolving the temporary plug and increasing the permeability and/or porosity of formations-l Particularly effective means of acidization of formations under discussion include use of the materials and methods described in the Dilgren US. Patents 3,307,630, 3,215,199 and 3,297,090.

The acidizing fluid as described is injected through wells penetrating the productive oil zone at a pressure normally less than the fracturing pressure and at a rate not dependent upon the creation of a fracture between the connecting pair of wells. The permeable zone thus formed is preferably not fractured until after acidization of the formation has establishedsuflicient permeability for a significant amount of fluid communication between wells, if fracturing appears to be attractive or desirable to improve or increase fluid communication.

Once a permeable and/or porous horizontal channel connecting a pair of wells penetrating an oil shale formation has been established, various thermal, pyrolysis, or explosive means such as hot fluid injection, e.g., steam, hot water and mixtures thereof, hot gases, e.g., air, gaseous hydrocarbons such as hot hydrogen sulfide and mixtures of hydrocarbons and hydrogen sulfide; solvents, e.g.,

. aliphatic and aromatic liquid hydrocarbons, such as ben-= zene, xylene, kerosene, etc., said solvents may be hot or cold as Well as conventional in situ combustion means such as injecting thermal energy to selected portions of the formation as well as various other means as described on pages 104 of the World Oil issue of January 1965 and US. Patents 3,105,545, 3,150,715, 3,208,516, 3,221,- 810 and 3,250,328 as well as exposives (liquid or solid) can be employed for fluidizing materialsfor recovering through the production well and processing it for oil recovery. However, the temporary plug can be removed by use of a simply undersaturated acid solution such as hydrochloric acid solution or the like.

A preferred method for treating productive zones of an underground formation in order to improve and stimulate oil recovery therefrom comprises injecting into the formation a 15% HCl supersaturated aqueous solution containing sulfamic acid and continuing the injection until the sulfamic acid plugs the formation sufliciently to reduce inflow to a desired state which can be determined by pressure changes or the like. Thereafter an undersaturated solution of 15% HCl is injected in which the plugging acid (sulfamic acid) is soluble or dissolvable and the process is continued until the less permeable por tion of the formation is acidized sufficiently to increase its permeability to essentially the same degree as the more permeable zone and continuing dissolution of the temporary plug or dry sulfamic acid until the productive zone is essentially uniformly permeable.

Once the well has been properly prepared by the process of the present invention, any driving fluids may be used to aid in recovery of the oil and include steam and/ or water which may contain surfactants such as ionic, cationic and/ or non-ionic surfactants, e.g., sulfonates, polyalkoxy phenols, and the like, as well as hydrocarbons such as lower hydrocarbons and mixtures thereof and/ or in situ combustion drives.

Treatment of formations by the process of this invention is equally effective on oil, gas or water injection wells and removing the temporary dry acid plug by any acid media is also effective.

The foregoing description of the invention is merely intended to be explanatory thereof. Various changes in the details of the described method may be made, within the scope of the appended claims, without departing from the spirit of the invention.

I claim as my invention: 1. An improved method for recovering hydrocarbons from underground formations having heterogeneous permeable zones traversed by a borehole, comprising:

forcing through the borehole and into the heterogeneous permeable productive zone a supersaturated fluid containing a dry acid and forming a temporary plug;

forcing through the borehole and into the temporary plugged zones an acidizing solution to increase the permeability of the less permeable area of the productive zone;

continuing acidizing the productive zone to remove the temporary plug by dissolution; and,

recovering oil from the oil-productive zone.

2. A method of claim 1 wherein the dry acid is selected from the group consisting of sulfamic, glycollic, fumaric, oxalic,1 citric, tartaric, p-hydroxy benzonic acids and mixtures thereof.

3. The method of claim 2 wherein the acidizing medium is one which is capable of completely dissolving the temporary plug of the dry acid selected from the group consisting of sulfamic, glycollic, fumaric, oxalic, citric,

r tartaric, p-hydroxy benzonic acids and mixtures thereof.

4. The method of claim 2 wherein the acidizing medi-- um is one which is capable of completely dissolving the: temporary plug of sulfamic acid.

5. The process of claim 4 wherein the fluid and acidiz-- ing medium is a 15% I-ICl solution.

6. The process of claim 3 wherein the fluid and acidizing medium is a mixture of HCl and HF.

7. The process of claim 3 wherein the fluid and acidizing medium is a 15 HCl solution.

(References on following page) 5 6 References Cited 3,141,501 7/1964 Bernard et al. 16642 X 3,261,400 7/1966 Elfrink l6630 UNITED STATES PATENTS 3,380,529 4/1968 Hendrickson. 4/1954 Bond et a1. 16642 X i 8/1957 Hower 166-42 X 5 STEPHEN J. NOVOSAD, Primary Examiner. 8/1957 Holbrook 166--42 X 11/1958 Carpenter 166. 29 US. Cl. X.R.

1/ 1959 Cocks 166-42 166-42 8/ 1959 Draper et a]. 166-42 X 7 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. L Y, 7 Dated December 2 4, 1968 Inventor(s) John MOOIB It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected as shown below:

' Column 5, line 29, change "benzonic" to benzoic.

Claim 2, line 5, change "benzonic" to benzoic.

Claim 5, line 5, change "benzonic" to benzoic.

ANA. "if-ii? DEC 1 Must:

fidwmlM-lilewhmlr- LARCSfiHg Offioer I.

Commission r l] 

